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 $134.95   12.282%   $151.5246   $151.52   $151.50   $151.50  
  Purchase #2 $190.87   5.303%   $200.9918   $200.99   $201.00   $201.00  
  Purchase #3 $156.98   5.339%   $165.3612   $165.36   $165.35   $165.40  
  Purchase #4 $112.92   7.845%   $121.7786   $121.78   $121.80   $121.80  
  Purchase #5 $151.46   3.157%   $156.2416   $156.24   $156.25   $156.20  
  Purchase #6 $53.59   11.604%   $59.8086   $59.81   $59.80   $59.80  
  Purchase #7 $151.73   10.581%   $167.7846   $167.78   $167.80   $167.80  
  7 purchase totals = $952.50       $1,023.4910   $1,023.48   $1,023.50   $1,023.50