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 $184.85   11.485%   $206.08   $206.08   $206.10   $206.10  
  Purchase #2 $241.68   6.561%   $257.5366   $257.54   $257.55   $257.50  
  Purchase #3 $133.49   9.762%   $146.5213   $146.52   $146.50   $146.50  
  Purchase #4 $132.86   13.390%   $150.65   $150.65   $150.65   $150.70  
  Purchase #5 $170.41   7.359%   $182.9505   $182.95   $182.95   $183.00  
  Purchase #6 $60.60   8.817%   $65.9431   $65.94   $65.95   $65.90  
  Purchase #7 $32.99   7.649%   $35.5134   $35.51   $35.50   $35.50  
  7 purchase totals = $956.88       $1,045.1949   $1,045.19   $1,045.20   $1,045.20