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 $204.98   3.567%   $212.2916   $212.29   $212.30   $212.30  
  Purchase #2 $249.30   8.663%   $270.8969   $270.90   $270.90   $270.90  
  Purchase #3 $25.73   11.776%   $28.76   $28.76   $28.75   $28.80  
  Purchase #4 $206.51   3.688%   $214.1261   $214.13   $214.15   $214.10  
  Purchase #5 $177.40   4.768%   $185.8584   $185.86   $185.85   $185.90  
  Purchase #6 $150.52   12.310%   $169.049   $169.05   $169.05   $169.00  
  Purchase #7 $10.51   6.428%   $11.1856   $11.19   $11.20   $11.20  
  7 purchase totals = $1,024.95       $1,092.1676   $1,092.18   $1,092.20   $1,092.20