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 $213.44   10.364%   $235.5609   $235.56   $235.55   $235.60  
  Purchase #2 $202.78   9.146%   $221.3263   $221.33   $221.35   $221.30  
  Purchase #3 $220.31   3.417%   $227.838   $227.84   $227.85   $227.80  
  Purchase #4 $70.90   4.360%   $73.9912   $73.99   $74.00   $74.00  
  Purchase #5 $207.75   8.379%   $225.1574   $225.16   $225.15   $225.20  
  Purchase #6 $230.56   9.252%   $251.8914   $251.89   $251.90   $251.90  
  Purchase #7 $85.57   5.412%   $90.201   $90.20   $90.20   $90.20  
  7 purchase totals = $1,231.31       $1,325.9662   $1,325.97   $1,326.00   $1,326.00