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 $75.26   12.521%   $84.6833   $84.68   $84.70   $84.70  
  Purchase #2 $131.54   11.458%   $146.6119   $146.61   $146.60   $146.60  
  Purchase #3 $112.56   13.424%   $127.6701   $127.67   $127.65   $127.70  
  Purchase #4 $5.74   3.860%   $5.9616   $5.96   $5.95   $6.00  
  Purchase #5 $63.30   7.168%   $67.8373   $67.84   $67.85   $67.80  
  Purchase #6 $238.54   13.545%   $270.8502   $270.85   $270.85   $270.90  
  Purchase #7 $106.78   5.589%   $112.7479   $112.75   $112.75   $112.70  
  7 purchase totals = $733.72       $816.3623   $816.36   $816.35   $816.40