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 $66.85   13.578%   $75.9269   $75.93   $75.95   $75.90  
  Purchase #2 $57.69   5.297%   $60.7458   $60.75   $60.75   $60.70  
  Purchase #3 $203.47   4.579%   $212.7869   $212.79   $212.80   $212.80  
  Purchase #4 $201.39   13.561%   $228.7005   $228.70   $228.70   $228.70  
  Purchase #5 $250.60   12.588%   $282.1455   $282.15   $282.15   $282.10  
  Purchase #6 $143.30   12.563%   $161.3028   $161.30   $161.30   $161.30  
  Purchase #7 $130.89   3.189%   $135.0641   $135.06   $135.05   $135.10  
  7 purchase totals = $1,054.19       $1,156.6725   $1,156.68   $1,156.70   $1,156.60