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 $186.68   8.832%   $203.1676   $203.17   $203.15   $203.20  
  Purchase #2 $200.82   6.211%   $213.2929   $213.29   $213.30   $213.30  
  Purchase #3 $80.67   11.538%   $89.9777   $89.98   $90.00   $90.00  
  Purchase #4 $248.31   6.600%   $264.6985   $264.70   $264.70   $264.70  
  Purchase #5 $124.35   6.874%   $132.8978   $132.90   $132.90   $132.90  
  Purchase #6 $212.80   11.534%   $237.3444   $237.34   $237.35   $237.30  
  Purchase #7 $200.35   9.818%   $220.0204   $220.02   $220.00   $220.00  
  7 purchase totals = $1,253.98       $1,361.3993   $1,361.40   $1,361.40   $1,361.40