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 $87.39   7.637%   $94.064   $94.06   $94.05   $94.10  
  Purchase #2 $232.28   11.699%   $259.4544   $259.45   $259.45   $259.50  
  Purchase #3 $173.65   6.492%   $184.9234   $184.92   $184.90   $184.90  
  Purchase #4 $62.73   6.781%   $66.9837   $66.98   $67.00   $67.00  
  Purchase #5 $160.42   8.167%   $173.5215   $173.52   $173.50   $173.50  
  Purchase #6 $218.97   5.317%   $230.6126   $230.61   $230.60   $230.60  
  Purchase #7 $50.58   5.194%   $53.2071   $53.21   $53.20   $53.20  
  7 purchase totals = $986.02       $1,062.7667   $1,062.75   $1,062.70   $1,062.80