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 $69.85   7.608%   $75.1642   $75.16   $75.15   $75.20  
  Purchase #2 $99.76   11.551%   $111.2833   $111.28   $111.30   $111.30  
  Purchase #3 $118.55   4.437%   $123.8101   $123.81   $123.80   $123.80  
  Purchase #4 $8.26   12.749%   $9.3131   $9.31   $9.30   $9.30  
  Purchase #5 $198.93   12.592%   $223.9793   $223.98   $224.00   $224.00  
  Purchase #6 $154.50   11.309%   $171.9724   $171.97   $171.95   $172.00  
  Purchase #7 $188.40   6.800%   $201.2112   $201.21   $201.20   $201.20  
  7 purchase totals = $838.25       $916.7336   $916.72   $916.70   $916.80