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 $34.57   6.272%   $36.7382   $36.74   $36.75   $36.70  
  Purchase #2 $171.72   9.194%   $187.5079   $187.51   $187.50   $187.50  
  Purchase #3 $25.68   7.164%   $27.5197   $27.52   $27.50   $27.50  
  Purchase #4 $120.35   10.140%   $132.5535   $132.55   $132.55   $132.60  
  Purchase #5 $218.78   12.367%   $245.8365   $245.84   $245.85   $245.80  
  Purchase #6 $52.53   11.469%   $58.5547   $58.55   $58.55   $58.60  
  Purchase #7 $64.67   11.753%   $72.2707   $72.27   $72.25   $72.30  
  7 purchase totals = $688.30       $760.9812   $760.98   $760.95   $761.00