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 $218.77   3.242%   $225.8625   $225.86   $225.85   $225.90  
  Purchase #2 $241.38   8.850%   $262.7421   $262.74   $262.75   $262.70  
  Purchase #3 $203.81   12.323%   $228.9255   $228.93   $228.95   $228.90  
  Purchase #4 $16.58   11.165%   $18.4312   $18.43   $18.45   $18.40  
  Purchase #5 $179.96   13.639%   $204.5047   $204.50   $204.50   $204.50  
  Purchase #6 $171.39   5.852%   $181.4197   $181.42   $181.40   $181.40  
  Purchase #7 $173.60   4.127%   $180.7645   $180.76   $180.75   $180.80  
  7 purchase totals = $1,205.49       $1,302.6502   $1,302.64   $1,302.65   $1,302.60