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 $76.64   10.653%   $84.8045   $84.80   $84.80   $84.80  
  Purchase #2 $91.28   12.434%   $102.6298   $102.63   $102.65   $102.60  
  Purchase #3 $240.72   4.257%   $250.9675   $250.97   $250.95   $251.00  
  Purchase #4 $138.88   4.536%   $145.1796   $145.18   $145.20   $145.20  
  Purchase #5 $67.26   12.275%   $75.5162   $75.52   $75.50   $75.50  
  Purchase #6 $247.33   13.868%   $281.6297   $281.63   $281.65   $281.60  
  Purchase #7 $66.97   7.160%   $71.7651   $71.77   $71.75   $71.80  
  7 purchase totals = $929.08       $1,012.4924   $1,012.50   $1,012.50   $1,012.50