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 $92.32   10.854%   $102.3404   $102.34   $102.35   $102.30  
  Purchase #2 $133.74   9.661%   $146.6606   $146.66   $146.65   $146.70  
  Purchase #3 $210.39   11.808%   $235.2329   $235.23   $235.25   $235.20  
  Purchase #4 $13.47   6.411%   $14.3336   $14.33   $14.35   $14.30  
  Purchase #5 $217.95   6.233%   $231.5348   $231.53   $231.55   $231.50  
  Purchase #6 $184.86   10.399%   $204.0836   $204.08   $204.10   $204.10  
  Purchase #7 $67.52   13.488%   $76.6271   $76.63   $76.65   $76.60  
  7 purchase totals = $920.25       $1,010.8130   $1,010.80   $1,010.90   $1,010.70