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 $250.64   5.471%   $264.3525   $264.35   $264.35   $264.40  
  Purchase #2 $66.53   11.392%   $74.1091   $74.11   $74.10   $74.10  
  Purchase #3 $60.80   12.872%   $68.6262   $68.63   $68.65   $68.60  
  Purchase #4 $234.60   8.300%   $254.0718   $254.07   $254.05   $254.10  
  Purchase #5 $54.85   6.224%   $58.2639   $58.26   $58.25   $58.30  
  Purchase #6 $232.82   8.288%   $252.1161   $252.12   $252.10   $252.10  
  Purchase #7 $84.67   5.622%   $89.4301   $89.43   $89.45   $89.40  
  7 purchase totals = $984.91       $1,060.9697   $1,060.97   $1,060.95   $1,061.00