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 $184.94   10.707%   $204.7415   $204.74   $204.75   $204.70  
  Purchase #2 $58.84   12.372%   $66.1197   $66.12   $66.10   $66.10  
  Purchase #3 $201.73   11.626%   $225.1831   $225.18   $225.20   $225.20  
  Purchase #4 $151.36   13.265%   $171.4379   $171.44   $171.45   $171.40  
  Purchase #5 $109.73   6.149%   $116.4773   $116.48   $116.50   $116.50  
  Purchase #6 $193.28   13.373%   $219.1273   $219.13   $219.15   $219.10  
  Purchase #7 $8.96   9.561%   $9.8167   $9.82   $9.80   $9.80  
  7 purchase totals = $908.84       $1,012.9035   $1,012.91   $1,012.95   $1,012.80