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 $89.35   13.727%   $101.6151   $101.62   $101.60   $101.60  
  Purchase #2 $102.95   12.714%   $116.0391   $116.04   $116.05   $116.00  
  Purchase #3 $56.46   7.170%   $60.5082   $60.51   $60.50   $60.50  
  Purchase #4 $199.52   4.300%   $208.0994   $208.10   $208.10   $208.10  
  Purchase #5 $196.68   7.800%   $212.021   $212.02   $212.00   $212.00  
  Purchase #6 $148.85   12.641%   $167.6661   $167.67   $167.65   $167.70  
  Purchase #7 $149.72   11.483%   $166.9123   $166.91   $166.90   $166.90  
  7 purchase totals = $943.53       $1,032.8612   $1,032.87   $1,032.80   $1,032.80