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 $164.52   11.588%   $183.5846   $183.58   $183.60   $183.60  
  Purchase #2 $56.74   5.691%   $59.9691   $59.97   $59.95   $60.00  
  Purchase #3 $200.52   10.850%   $222.2764   $222.28   $222.30   $222.30  
  Purchase #4 $219.75   3.572%   $227.5995   $227.60   $227.60   $227.60  
  Purchase #5 $221.99   10.318%   $244.8949   $244.89   $244.90   $244.90  
  Purchase #6 $161.42   12.270%   $181.2262   $181.23   $181.25   $181.20  
  Purchase #7 $135.82   10.775%   $150.4546   $150.45   $150.45   $150.50  
  7 purchase totals = $1,160.76       $1,270.0053   $1,270.00   $1,270.05   $1,270.10