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 $240.78   11.700%   $268.9513   $268.95   $268.95   $269.00  
  Purchase #2 $205.53   8.832%   $223.6824   $223.68   $223.70   $223.70  
  Purchase #3 $110.82   6.779%   $118.3325   $118.33   $118.35   $118.30  
  Purchase #4 $206.57   9.755%   $226.7209   $226.72   $226.70   $226.70  
  Purchase #5 $212.56   13.841%   $241.9804   $241.98   $242.00   $242.00  
  Purchase #6 $209.67   10.734%   $232.176   $232.18   $232.20   $232.20  
  Purchase #7 $48.38   10.477%   $53.4488   $53.45   $53.45   $53.40  
  7 purchase totals = $1,234.31       $1,365.2923   $1,365.29   $1,365.35   $1,365.30