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 $217.79   13.746%   $247.7274   $247.73   $247.75   $247.70  
  Purchase #2 $43.99   11.672%   $49.1245   $49.12   $49.10   $49.10  
  Purchase #3 $158.32   4.502%   $165.4476   $165.45   $165.45   $165.40  
  Purchase #4 $228.41   9.874%   $250.9632   $250.96   $250.95   $251.00  
  Purchase #5 $244.46   11.538%   $272.6658   $272.67   $272.65   $272.70  
  Purchase #6 $57.77   9.662%   $63.3517   $63.35   $63.35   $63.40  
  Purchase #7 $201.52   7.189%   $216.0073   $216.01   $216.00   $216.00  
  7 purchase totals = $1,152.26       $1,265.2875   $1,265.29   $1,265.25   $1,265.30