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 $246.27   11.772%   $275.2609   $275.26   $275.25   $275.30  
  Purchase #2 $94.76   9.187%   $103.4656   $103.47   $103.45   $103.50  
  Purchase #3 $129.88   4.356%   $135.5376   $135.54   $135.55   $135.50  
  Purchase #4 $180.91   4.783%   $189.5629   $189.56   $189.55   $189.60  
  Purchase #5 $113.62   12.687%   $128.035   $128.04   $128.05   $128.00  
  Purchase #6 $119.60   5.564%   $126.2545   $126.25   $126.25   $126.30  
  Purchase #7 $181.42   12.817%   $204.6726   $204.67   $204.65   $204.70  
  7 purchase totals = $1,066.46       $1,162.7891   $1,162.79   $1,162.75   $1,162.90