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 $240.95   10.673%   $266.6666   $266.67   $266.65   $266.70  
  Purchase #2 $41.55   8.312%   $45.0036   $45.00   $45.00   $45.00  
  Purchase #3 $110.29   5.174%   $115.9964   $116.00   $116.00   $116.00  
  Purchase #4 $238.97   10.839%   $264.872   $264.87   $264.85   $264.90  
  Purchase #5 $34.49   6.419%   $36.7039   $36.70   $36.70   $36.70  
  Purchase #6 $78.83   6.718%   $84.1258   $84.13   $84.15   $84.10  
  Purchase #7 $221.32   4.753%   $231.8393   $231.84   $231.85   $231.80  
  7 purchase totals = $966.40       $1,045.2076   $1,045.21   $1,045.20   $1,045.20