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 $228.69   8.104%   $247.223   $247.22   $247.20   $247.20  
  Purchase #2 $49.31   7.453%   $52.9851   $52.99   $53.00   $53.00  
  Purchase #3 $120.66   3.644%   $125.0569   $125.06   $125.05   $125.10  
  Purchase #4 $236.37   11.258%   $262.9805   $262.98   $263.00   $263.00  
  Purchase #5 $88.67   11.457%   $98.8289   $98.83   $98.85   $98.80  
  Purchase #6 $5.74   9.201%   $6.2681   $6.27   $6.25   $6.30  
  Purchase #7 $149.67   12.300%   $168.0794   $168.08   $168.10   $168.10  
  7 purchase totals = $879.11       $961.4219   $961.43   $961.45   $961.50