Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.60   3.802%   $201.9987   $202.00   $202.00   $202.00  
  Purchase #2 $136.97   12.170%   $153.6392   $153.64   $153.65   $153.60  
  Purchase #3 $95.26   12.165%   $106.8484   $106.85   $106.85   $106.80  
  Purchase #4 $149.29   7.405%   $160.3449   $160.34   $160.35   $160.30  
  Purchase #5 $106.84   4.767%   $111.9331   $111.93   $111.95   $111.90  
  Purchase #6 $149.45   10.375%   $164.9554   $164.96   $164.95   $165.00  
  Purchase #7 $162.64   10.128%   $179.1122   $179.11   $179.10   $179.10  
  7 purchase totals = $995.05       $1,078.8319   $1,078.83   $1,078.85   $1,078.70