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 $246.33   7.111%   $263.8465   $263.85   $263.85   $263.80  
  Purchase #2 $45.96   6.289%   $48.8504   $48.85   $48.85   $48.90  
  Purchase #3 $202.42   4.854%   $212.2455   $212.25   $212.25   $212.20  
  Purchase #4 $178.59   4.864%   $187.2766   $187.28   $187.30   $187.30  
  Purchase #5 $96.73   13.829%   $110.1068   $110.11   $110.10   $110.10  
  Purchase #6 $127.56   13.521%   $144.8074   $144.81   $144.80   $144.80  
  Purchase #7 $205.90   7.811%   $221.9828   $221.98   $222.00   $222.00  
  7 purchase totals = $1,103.49       $1,189.1160   $1,189.13   $1,189.15   $1,189.10