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 $244.35   13.371%   $277.022   $277.02   $277.00   $277.00  
  Purchase #2 $9.90   12.575%   $11.1449   $11.14   $11.15   $11.10  
  Purchase #3 $145.75   10.170%   $160.5728   $160.57   $160.55   $160.60  
  Purchase #4 $119.95   12.655%   $135.1297   $135.13   $135.15   $135.10  
  Purchase #5 $167.40   4.496%   $174.9263   $174.93   $174.95   $174.90  
  Purchase #6 $221.80   11.521%   $247.3536   $247.35   $247.35   $247.40  
  Purchase #7 $203.88   8.148%   $220.4921   $220.49   $220.50   $220.50  
  7 purchase totals = $1,113.03       $1,226.6414   $1,226.63   $1,226.65   $1,226.60