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 $88.47   10.747%   $97.9779   $97.98   $98.00   $98.00  
  Purchase #2 $65.77   12.232%   $73.815   $73.82   $73.80   $73.80  
  Purchase #3 $95.91   10.836%   $106.3028   $106.30   $106.30   $106.30  
  Purchase #4 $212.40   3.253%   $219.3094   $219.31   $219.30   $219.30  
  Purchase #5 $219.53   8.720%   $238.673   $238.67   $238.65   $238.70  
  Purchase #6 $121.37   6.854%   $129.6887   $129.69   $129.70   $129.70  
  Purchase #7 $181.96   9.374%   $199.0169   $199.02   $199.00   $199.00  
  7 purchase totals = $985.41       $1,064.7837   $1,064.79   $1,064.75   $1,064.80