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 $200.97   9.517%   $220.0963   $220.10   $220.10   $220.10  
  Purchase #2 $196.75   7.747%   $211.9922   $211.99   $212.00   $212.00  
  Purchase #3 $59.47   5.574%   $62.7849   $62.78   $62.80   $62.80  
  Purchase #4 $211.84   12.370%   $238.0446   $238.04   $238.05   $238.00  
  Purchase #5 $179.80   12.706%   $202.6454   $202.65   $202.65   $202.60  
  Purchase #6 $228.64   6.346%   $243.1495   $243.15   $243.15   $243.10  
  Purchase #7 $180.88   11.174%   $201.0915   $201.09   $201.10   $201.10  
  7 purchase totals = $1,258.35       $1,379.8044   $1,379.80   $1,379.85   $1,379.70