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 $70.33   6.228%   $74.7102   $74.71   $74.70   $74.70  
  Purchase #2 $116.98   13.410%   $132.667   $132.67   $132.65   $132.70  
  Purchase #3 $191.74   7.627%   $206.364   $206.36   $206.35   $206.40  
  Purchase #4 $67.92   7.765%   $73.194   $73.19   $73.20   $73.20  
  Purchase #5 $211.32   9.852%   $232.1392   $232.14   $232.15   $232.10  
  Purchase #6 $209.31   11.660%   $233.7155   $233.72   $233.70   $233.70  
  Purchase #7 $102.55   6.303%   $109.0137   $109.01   $109.00   $109.00  
  7 purchase totals = $970.15       $1,061.8036   $1,061.80   $1,061.75   $1,061.80