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 $60.95   8.832%   $66.3331   $66.33   $66.35   $66.30  
  Purchase #2 $112.27   8.532%   $121.8489   $121.85   $121.85   $121.80  
  Purchase #3 $86.73   8.599%   $94.1879   $94.19   $94.20   $94.20  
  Purchase #4 $28.52   13.390%   $32.3388   $32.34   $32.35   $32.30  
  Purchase #5 $92.56   7.555%   $99.5529   $99.55   $99.55   $99.60  
  Purchase #6 $124.62   4.747%   $130.5357   $130.54   $130.55   $130.50  
  Purchase #7 $145.96   6.334%   $155.2051   $155.21   $155.20   $155.20  
  7 purchase totals = $651.61       $700.0024   $700.01   $700.05   $699.90