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 $134.32   5.852%   $142.1804   $142.18   $142.20   $142.20  
  Purchase #2 $205.77   11.801%   $230.0529   $230.05   $230.05   $230.10  
  Purchase #3 $194.43   13.625%   $220.9211   $220.92   $220.90   $220.90  
  Purchase #4 $128.35   4.176%   $133.7099   $133.71   $133.70   $133.70  
  Purchase #5 $88.92   4.561%   $92.9756   $92.98   $93.00   $93.00  
  Purchase #6 $88.60   8.499%   $96.1301   $96.13   $96.15   $96.10  
  Purchase #7 $30.33   6.765%   $32.3818   $32.38   $32.40   $32.40  
  7 purchase totals = $870.72       $948.3518   $948.35   $948.40   $948.40