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 $85.66   13.218%   $96.9825   $96.98   $97.00   $97.00  
  Purchase #2 $208.52   10.700%   $230.8316   $230.83   $230.85   $230.80  
  Purchase #3 $109.53   11.426%   $122.0449   $122.04   $122.05   $122.00  
  Purchase #4 $167.89   13.115%   $189.9088   $189.91   $189.90   $189.90  
  Purchase #5 $126.60   7.786%   $136.4571   $136.46   $136.45   $136.50  
  Purchase #6 $88.65   6.391%   $94.3156   $94.32   $94.30   $94.30  
  Purchase #7 $219.26   12.636%   $246.9657   $246.97   $246.95   $247.00  
  7 purchase totals = $1,006.11       $1,117.5062   $1,117.51   $1,117.50   $1,117.50