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 $225.99   9.181%   $246.7381   $246.74   $246.75   $246.70  
  Purchase #2 $157.58   10.619%   $174.3134   $174.31   $174.30   $174.30  
  Purchase #3 $168.60   5.452%   $177.7921   $177.79   $177.80   $177.80  
  Purchase #4 $25.71   7.435%   $27.6215   $27.62   $27.60   $27.60  
  Purchase #5 $181.67   12.843%   $205.0019   $205.00   $205.00   $205.00  
  Purchase #6 $6.96   9.492%   $7.6206   $7.62   $7.60   $7.60  
  Purchase #7 $232.53   9.727%   $255.1482   $255.15   $255.15   $255.10  
  7 purchase totals = $999.04       $1,094.2358   $1,094.23   $1,094.20   $1,094.10