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 $90.52   5.596%   $95.5855   $95.59   $95.60   $95.60  
  Purchase #2 $21.38   13.480%   $24.262   $24.26   $24.25   $24.30  
  Purchase #3 $121.39   11.623%   $135.4992   $135.50   $135.50   $135.50  
  Purchase #4 $139.59   11.824%   $156.0951   $156.10   $156.10   $156.10  
  Purchase #5 $176.50   9.582%   $193.4122   $193.41   $193.40   $193.40  
  Purchase #6 $149.85   4.796%   $157.0368   $157.04   $157.05   $157.00  
  Purchase #7 $232.37   10.790%   $257.4427   $257.44   $257.45   $257.40  
  7 purchase totals = $931.60       $1,019.3335   $1,019.34   $1,019.35   $1,019.30