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 $173.53   11.343%   $193.2135   $193.21   $193.20   $193.20  
  Purchase #2 $60.37   8.258%   $65.3554   $65.36   $65.35   $65.40  
  Purchase #3 $48.75   12.643%   $54.9135   $54.91   $54.90   $54.90  
  Purchase #4 $103.98   11.734%   $116.181   $116.18   $116.20   $116.20  
  Purchase #5 $53.61   12.828%   $60.4871   $60.49   $60.50   $60.50  
  Purchase #6 $71.57   12.586%   $80.5778   $80.58   $80.60   $80.60  
  Purchase #7 $204.29   6.220%   $216.9968   $217.00   $217.00   $217.00  
  7 purchase totals = $716.10       $787.7251   $787.73   $787.75   $787.80