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 $88.35   9.275%   $96.5445   $96.54   $96.55   $96.50  
  Purchase #2 $150.94   13.632%   $171.5161   $171.52   $171.50   $171.50  
  Purchase #3 $161.53   9.391%   $176.6993   $176.70   $176.70   $176.70  
  Purchase #4 $129.37   11.674%   $144.4727   $144.47   $144.45   $144.50  
  Purchase #5 $142.34   7.591%   $153.145   $153.15   $153.15   $153.10  
  Purchase #6 $124.92   8.202%   $135.1659   $135.17   $135.15   $135.20  
  Purchase #7 $155.74   4.430%   $162.6393   $162.64   $162.65   $162.60  
  7 purchase totals = $953.19       $1,040.1828   $1,040.19   $1,040.15   $1,040.10