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 $96.92   7.262%   $103.9583   $103.96   $103.95   $104.00  
  Purchase #2 $26.44   10.832%   $29.304   $29.30   $29.30   $29.30  
  Purchase #3 $207.81   3.276%   $214.6179   $214.62   $214.60   $214.60  
  Purchase #4 $91.50   4.603%   $95.7117   $95.71   $95.70   $95.70  
  Purchase #5 $95.70   6.837%   $102.243   $102.24   $102.25   $102.20  
  Purchase #6 $209.51   13.869%   $238.5669   $238.57   $238.55   $238.60  
  Purchase #7 $110.52   7.367%   $118.662   $118.66   $118.65   $118.70  
  7 purchase totals = $838.40       $903.0638   $903.06   $903.00   $903.10