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 $214.54   13.310%   $243.0953   $243.10   $243.10   $243.10  
  Purchase #2 $205.85   4.383%   $214.8724   $214.87   $214.85   $214.90  
  Purchase #3 $41.70   4.556%   $43.5999   $43.60   $43.60   $43.60  
  Purchase #4 $138.33   12.581%   $155.7333   $155.73   $155.75   $155.70  
  Purchase #5 $91.47   6.355%   $97.2829   $97.28   $97.30   $97.30  
  Purchase #6 $232.72   11.221%   $258.8335   $258.83   $258.85   $258.80  
  Purchase #7 $72.85   3.507%   $75.4048   $75.40   $75.40   $75.40  
  7 purchase totals = $997.46       $1,088.8221   $1,088.81   $1,088.85   $1,088.80