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 $206.60   8.591%   $224.349   $224.35   $224.35   $224.30  
  Purchase #2 $12.42   10.309%   $13.7004   $13.70   $13.70   $13.70  
  Purchase #3 $207.58   12.239%   $232.9857   $232.99   $233.00   $233.00  
  Purchase #4 $174.96   9.347%   $191.3135   $191.31   $191.30   $191.30  
  Purchase #5 $93.36   3.267%   $96.4101   $96.41   $96.40   $96.40  
  Purchase #6 $167.70   7.570%   $180.3949   $180.39   $180.40   $180.40  
  Purchase #7 $85.26   12.399%   $95.8314   $95.83   $95.85   $95.80  
  7 purchase totals = $947.88       $1,034.9850   $1,034.98   $1,035.00   $1,034.90