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 $157.58   11.131%   $175.1202   $175.12   $175.10   $175.10  
  Purchase #2 $75.61   10.255%   $83.3638   $83.36   $83.35   $83.40  
  Purchase #3 $78.59   12.566%   $88.4656   $88.47   $88.45   $88.50  
  Purchase #4 $229.73   7.175%   $246.2131   $246.21   $246.20   $246.20  
  Purchase #5 $148.91   5.421%   $156.9824   $156.98   $157.00   $157.00  
  Purchase #6 $183.46   10.648%   $202.9948   $202.99   $203.00   $203.00  
  Purchase #7 $120.56   8.189%   $130.4327   $130.43   $130.45   $130.40  
  7 purchase totals = $994.44       $1,083.5726   $1,083.56   $1,083.55   $1,083.60