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 $92.65   4.385%   $96.7127   $96.71   $96.70   $96.70  
  Purchase #2 $179.43   13.568%   $203.7751   $203.78   $203.80   $203.80  
  Purchase #3 $119.75   6.148%   $127.1122   $127.11   $127.10   $127.10  
  Purchase #4 $60.98   3.803%   $63.2991   $63.30   $63.30   $63.30  
  Purchase #5 $226.71   11.559%   $252.9154   $252.92   $252.90   $252.90  
  Purchase #6 $26.30   10.189%   $28.9797   $28.98   $29.00   $29.00  
  Purchase #7 $78.53   12.590%   $88.4169   $88.42   $88.40   $88.40  
  7 purchase totals = $784.35       $861.2111   $861.22   $861.20   $861.20