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 $75.64   11.752%   $84.5292   $84.53   $84.55   $84.50  
  Purchase #2 $224.57   9.168%   $245.1586   $245.16   $245.15   $245.20  
  Purchase #3 $112.57   13.610%   $127.8908   $127.89   $127.90   $127.90  
  Purchase #4 $245.29   9.463%   $268.5018   $268.50   $268.50   $268.50  
  Purchase #5 $20.98   11.222%   $23.3344   $23.33   $23.35   $23.30  
  Purchase #6 $220.60   12.204%   $247.522   $247.52   $247.50   $247.50  
  Purchase #7 $146.97   4.593%   $153.7203   $153.72   $153.70   $153.70  
  7 purchase totals = $1,046.62       $1,150.6571   $1,150.65   $1,150.65   $1,150.60