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 $67.96   11.782%   $75.967   $75.97   $75.95   $76.00  
  Purchase #2 $11.74   11.594%   $13.1011   $13.10   $13.10   $13.10  
  Purchase #3 $12.39   10.167%   $13.6497   $13.65   $13.65   $13.60  
  Purchase #4 $145.91   12.801%   $164.5879   $164.59   $164.60   $164.60  
  Purchase #5 $83.47   8.773%   $90.7928   $90.79   $90.80   $90.80  
  Purchase #6 $243.53   10.869%   $269.9993   $270.00   $270.00   $270.00  
  Purchase #7 $214.25   10.717%   $237.2112   $237.21   $237.20   $237.20  
  7 purchase totals = $779.25       $865.3090   $865.31   $865.30   $865.30