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 $65.45   13.421%   $74.234   $74.23   $74.25   $74.20  
  Purchase #2 $212.26   10.765%   $235.1098   $235.11   $235.10   $235.10  
  Purchase #3 $131.33   12.118%   $147.2446   $147.24   $147.25   $147.20  
  Purchase #4 $70.33   10.376%   $77.6274   $77.63   $77.65   $77.60  
  Purchase #5 $250.43   8.835%   $272.5555   $272.56   $272.55   $272.60  
  Purchase #6 $24.25   5.427%   $25.566   $25.57   $25.55   $25.60  
  Purchase #7 $190.89   6.610%   $203.5078   $203.51   $203.50   $203.50  
  7 purchase totals = $944.94       $1,035.8451   $1,035.85   $1,035.85   $1,035.80