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 $162.82   13.350%   $184.5565   $184.56   $184.55   $184.60  
  Purchase #2 $250.96   3.820%   $260.5467   $260.55   $260.55   $260.50  
  Purchase #3 $61.45   13.519%   $69.7574   $69.76   $69.75   $69.80  
  Purchase #4 $149.99   10.856%   $166.2729   $166.27   $166.25   $166.30  
  Purchase #5 $187.33   9.386%   $204.9128   $204.91   $204.90   $204.90  
  Purchase #6 $81.49   3.507%   $84.3479   $84.35   $84.35   $84.30  
  Purchase #7 $108.76   13.777%   $123.7439   $123.74   $123.75   $123.70  
  7 purchase totals = $1,002.80       $1,094.1381   $1,094.14   $1,094.10   $1,094.10