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 $52.90   12.650%   $59.5919   $59.59   $59.60   $59.60  
  Purchase #2 $49.95   5.297%   $52.5959   $52.60   $52.60   $52.60  
  Purchase #3 $240.29   11.419%   $267.7287   $267.73   $267.75   $267.70  
  Purchase #4 $95.61   7.223%   $102.5159   $102.52   $102.50   $102.50  
  Purchase #5 $210.54   4.663%   $220.3575   $220.36   $220.35   $220.40  
  Purchase #6 $141.52   11.411%   $157.6688   $157.67   $157.65   $157.70  
  Purchase #7 $219.40   4.243%   $228.7091   $228.71   $228.70   $228.70  
  7 purchase totals = $1,010.21       $1,089.1678   $1,089.18   $1,089.15   $1,089.20