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 $212.99   9.397%   $233.0047   $233.00   $233.00   $233.00  
  Purchase #2 $132.95   6.451%   $141.5266   $141.53   $141.55   $141.50  
  Purchase #3 $250.82   5.497%   $264.6076   $264.61   $264.60   $264.60  
  Purchase #4 $200.39   9.542%   $219.5112   $219.51   $219.50   $219.50  
  Purchase #5 $220.80   10.372%   $243.7014   $243.70   $243.70   $243.70  
  Purchase #6 $51.74   8.165%   $55.9646   $55.96   $55.95   $56.00  
  Purchase #7 $160.77   5.793%   $170.0834   $170.08   $170.10   $170.10  
  7 purchase totals = $1,230.46       $1,328.3995   $1,328.39   $1,328.40   $1,328.40