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 $68.53   3.671%   $71.0457   $71.05   $71.05   $71.00  
  Purchase #2 $144.72   5.722%   $153.0009   $153.00   $153.00   $153.00  
  Purchase #3 $63.34   11.249%   $70.4651   $70.47   $70.45   $70.50  
  Purchase #4 $196.69   7.501%   $211.4437   $211.44   $211.45   $211.40  
  Purchase #5 $145.56   13.220%   $164.803   $164.80   $164.80   $164.80  
  Purchase #6 $225.94   9.187%   $246.6971   $246.70   $246.70   $246.70  
  Purchase #7 $96.65   9.856%   $106.1758   $106.18   $106.20   $106.20  
  7 purchase totals = $941.43       $1,023.6313   $1,023.64   $1,023.65   $1,023.60