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 $88.69   10.149%   $97.6911   $97.69   $97.70   $97.70  
  Purchase #2 $94.46   5.180%   $99.353   $99.35   $99.35   $99.40  
  Purchase #3 $167.75   9.293%   $183.339   $183.34   $183.35   $183.30  
  Purchase #4 $150.52   6.197%   $159.8477   $159.85   $159.85   $159.80  
  Purchase #5 $187.27   10.568%   $207.0607   $207.06   $207.05   $207.10  
  Purchase #6 $147.53   11.635%   $164.6951   $164.70   $164.70   $164.70  
  Purchase #7 $235.37   12.411%   $264.5818   $264.58   $264.60   $264.60  
  7 purchase totals = $1,071.59       $1,176.5684   $1,176.57   $1,176.60   $1,176.60