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 $204.47   3.160%   $210.9313   $210.93   $210.95   $210.90  
  Purchase #2 $17.70   9.796%   $19.4339   $19.43   $19.45   $19.40  
  Purchase #3 $169.94   3.291%   $175.5327   $175.53   $175.55   $175.50  
  Purchase #4 $171.82   13.286%   $194.648   $194.65   $194.65   $194.60  
  Purchase #5 $203.63   4.243%   $212.27   $212.27   $212.25   $212.30  
  Purchase #6 $77.46   8.162%   $83.7823   $83.78   $83.80   $83.80  
  Purchase #7 $63.31   9.505%   $69.3276   $69.33   $69.35   $69.30  
  7 purchase totals = $908.33       $965.9258   $965.92   $966.00   $965.80