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 $41.26   11.495%   $46.0028   $46.00   $46.00   $46.00  
  Purchase #2 $149.52   9.817%   $164.1984   $164.20   $164.20   $164.20  
  Purchase #3 $194.64   4.791%   $203.9652   $203.97   $203.95   $204.00  
  Purchase #4 $62.42   10.355%   $68.8836   $68.88   $68.90   $68.90  
  Purchase #5 $167.77   10.234%   $184.9396   $184.94   $184.95   $184.90  
  Purchase #6 $116.27   5.351%   $122.4916   $122.49   $122.50   $122.50  
  Purchase #7 $139.60   5.557%   $147.3576   $147.36   $147.35   $147.40  
  7 purchase totals = $871.48       $937.8388   $937.84   $937.85   $937.90