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 $136.90   7.352%   $146.9649   $146.96   $146.95   $147.00  
  Purchase #2 $23.99   8.415%   $26.0088   $26.01   $26.00   $26.00  
  Purchase #3 $250.33   11.547%   $279.2356   $279.24   $279.25   $279.20  
  Purchase #4 $88.53   5.384%   $93.2965   $93.30   $93.30   $93.30  
  Purchase #5 $211.95   3.661%   $219.7095   $219.71   $219.70   $219.70  
  Purchase #6 $149.38   9.131%   $163.0199   $163.02   $163.00   $163.00  
  Purchase #7 $172.78   7.473%   $185.6918   $185.69   $185.70   $185.70  
  7 purchase totals = $1,033.86       $1,113.9270   $1,113.93   $1,113.90   $1,113.90