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 $228.31   13.472%   $259.0679   $259.07   $259.05   $259.10  
  Purchase #2 $88.54   3.277%   $91.4415   $91.44   $91.45   $91.40  
  Purchase #3 $204.44   6.398%   $217.5201   $217.52   $217.50   $217.50  
  Purchase #4 $45.55   8.183%   $49.2774   $49.28   $49.30   $49.30  
  Purchase #5 $157.44   10.822%   $174.4782   $174.48   $174.50   $174.50  
  Purchase #6 $127.32   10.220%   $140.3321   $140.33   $140.35   $140.30  
  Purchase #7 $227.93   6.179%   $242.0138   $242.01   $242.00   $242.00  
  7 purchase totals = $1,079.53       $1,174.1310   $1,174.13   $1,174.15   $1,174.10