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 $228.94   5.836%   $242.3009   $242.30   $242.30   $242.30  
  Purchase #2 $220.41   6.872%   $235.5566   $235.56   $235.55   $235.60  
  Purchase #3 $53.97   8.255%   $58.4252   $58.43   $58.45   $58.40  
  Purchase #4 $237.36   6.679%   $253.2133   $253.21   $253.20   $253.20  
  Purchase #5 $97.30   11.582%   $108.5693   $108.57   $108.55   $108.60  
  Purchase #6 $123.67   12.367%   $138.9643   $138.96   $138.95   $139.00  
  Purchase #7 $71.38   6.615%   $76.1018   $76.10   $76.10   $76.10  
  7 purchase totals = $1,033.03       $1,113.1314   $1,113.13   $1,113.10   $1,113.20