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 $116.28   7.212%   $124.6661   $124.67   $124.65   $124.70  
  Purchase #2 $206.99   4.760%   $216.8427   $216.84   $216.85   $216.80  
  Purchase #3 $207.60   9.277%   $226.8591   $226.86   $226.85   $226.90  
  Purchase #4 $190.78   8.570%   $207.1298   $207.13   $207.15   $207.10  
  Purchase #5 $230.98   4.742%   $241.9331   $241.93   $241.95   $241.90  
  Purchase #6 $85.86   10.489%   $94.8659   $94.87   $94.85   $94.90  
  Purchase #7 $226.25   13.140%   $255.9793   $255.98   $256.00   $256.00  
  7 purchase totals = $1,264.74       $1,368.2760   $1,368.28   $1,368.30   $1,368.30