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 $141.95   5.483%   $149.7331   $149.73   $149.75   $149.70  
  Purchase #2 $93.43   3.525%   $96.7234   $96.72   $96.70   $96.70  
  Purchase #3 $211.47   6.548%   $225.3171   $225.32   $225.30   $225.30  
  Purchase #4 $66.43   6.229%   $70.5679   $70.57   $70.55   $70.60  
  Purchase #5 $245.60   8.600%   $266.7216   $266.72   $266.70   $266.70  
  Purchase #6 $233.43   4.183%   $243.1944   $243.19   $243.20   $243.20  
  Purchase #7 $191.45   3.548%   $198.2426   $198.24   $198.25   $198.20  
  7 purchase totals = $1,183.76       $1,250.5001   $1,250.49   $1,250.45   $1,250.40