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 $213.52   13.722%   $242.8192   $242.82   $242.80   $242.80  
  Purchase #2 $135.95   4.156%   $141.6001   $141.60   $141.60   $141.60  
  Purchase #3 $39.98   12.452%   $44.9583   $44.96   $44.95   $45.00  
  Purchase #4 $181.72   8.604%   $197.3552   $197.36   $197.35   $197.40  
  Purchase #5 $11.92   6.223%   $12.6618   $12.66   $12.65   $12.70  
  Purchase #6 $148.31   4.796%   $155.4229   $155.42   $155.40   $155.40  
  Purchase #7 $60.96   11.174%   $67.7717   $67.77   $67.75   $67.80  
  7 purchase totals = $792.36       $862.5892   $862.59   $862.50   $862.70