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 $232.98   13.602%   $264.6699   $264.67   $264.65   $264.70  
  Purchase #2 $213.96   4.675%   $223.9626   $223.96   $223.95   $224.00  
  Purchase #3 $197.45   11.597%   $220.3483   $220.35   $220.35   $220.30  
  Purchase #4 $58.28   4.586%   $60.9527   $60.95   $60.95   $61.00  
  Purchase #5 $107.61   5.367%   $113.3854   $113.39   $113.40   $113.40  
  Purchase #6 $110.36   11.288%   $122.8174   $122.82   $122.80   $122.80  
  Purchase #7 $230.26   6.324%   $244.8216   $244.82   $244.80   $244.80  
  7 purchase totals = $1,150.90       $1,250.9579   $1,250.96   $1,250.90   $1,251.00