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 $34.63   7.449%   $37.2096   $37.21   $37.20   $37.20  
  Purchase #2 $166.94   6.583%   $177.9297   $177.93   $177.95   $177.90  
  Purchase #3 $209.59   7.474%   $225.2548   $225.25   $225.25   $225.30  
  Purchase #4 $150.47   9.790%   $165.201   $165.20   $165.20   $165.20  
  Purchase #5 $244.27   3.134%   $251.9254   $251.93   $251.95   $251.90  
  Purchase #6 $163.92   11.642%   $183.0036   $183.00   $183.00   $183.00  
  Purchase #7 $138.73   9.333%   $151.6777   $151.68   $151.70   $151.70  
  7 purchase totals = $1,108.55       $1,192.2018   $1,192.20   $1,192.25   $1,192.20