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 $201.27   13.337%   $228.1134   $228.11   $228.10   $228.10  
  Purchase #2 $124.57   7.843%   $134.34   $134.34   $134.35   $134.30  
  Purchase #3 $46.87   4.260%   $48.8667   $48.87   $48.85   $48.90  
  Purchase #4 $181.83   6.556%   $193.7508   $193.75   $193.75   $193.80  
  Purchase #5 $218.37   12.183%   $244.974   $244.97   $244.95   $245.00  
  Purchase #6 $122.42   10.504%   $135.279   $135.28   $135.30   $135.30  
  Purchase #7 $178.62   9.581%   $195.7336   $195.73   $195.75   $195.70  
  7 purchase totals = $1,073.95       $1,181.0575   $1,181.05   $1,181.05   $1,181.10