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 $69.34   7.742%   $74.7083   $74.71   $74.70   $74.70  
  Purchase #2 $155.61   11.472%   $173.4616   $173.46   $173.45   $173.50  
  Purchase #3 $201.57   6.732%   $215.1397   $215.14   $215.15   $215.10  
  Purchase #4 $5.36   11.163%   $5.9583   $5.96   $5.95   $6.00  
  Purchase #5 $223.40   12.506%   $251.3384   $251.34   $251.35   $251.30  
  Purchase #6 $76.71   12.837%   $86.5573   $86.56   $86.55   $86.60  
  Purchase #7 $80.67   9.109%   $88.0182   $88.02   $88.00   $88.00  
  7 purchase totals = $812.66       $895.1818   $895.19   $895.15   $895.20