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 $59.68   10.196%   $65.765   $65.77   $65.75   $65.80  
  Purchase #2 $170.77   6.316%   $181.5558   $181.56   $181.55   $181.60  
  Purchase #3 $195.64   8.693%   $212.647   $212.65   $212.65   $212.60  
  Purchase #4 $39.96   11.332%   $44.4883   $44.49   $44.50   $44.50  
  Purchase #5 $84.71   13.831%   $96.4262   $96.43   $96.45   $96.40  
  Purchase #6 $115.99   12.183%   $130.1211   $130.12   $130.10   $130.10  
  Purchase #7 $64.93   5.196%   $68.3038   $68.30   $68.30   $68.30  
  7 purchase totals = $731.68       $799.3072   $799.32   $799.30   $799.30