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 $204.69   3.741%   $212.3475   $212.35   $212.35   $212.30  
  Purchase #2 $218.56   10.617%   $241.7645   $241.76   $241.75   $241.80  
  Purchase #3 $228.88   11.400%   $254.9723   $254.97   $254.95   $255.00  
  Purchase #4 $166.30   3.369%   $171.9026   $171.90   $171.90   $171.90  
  Purchase #5 $159.79   12.602%   $179.9267   $179.93   $179.95   $179.90  
  Purchase #6 $41.58   12.593%   $46.8162   $46.82   $46.80   $46.80  
  Purchase #7 $194.80   11.224%   $216.6644   $216.66   $216.65   $216.70  
  7 purchase totals = $1,214.60       $1,324.3942   $1,324.39   $1,324.35   $1,324.40