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 $191.72   7.255%   $205.6293   $205.63   $205.65   $205.60  
  Purchase #2 $123.45   12.760%   $139.2022   $139.20   $139.20   $139.20  
  Purchase #3 $26.47   3.293%   $27.3417   $27.34   $27.35   $27.30  
  Purchase #4 $70.61   7.262%   $75.7377   $75.74   $75.75   $75.70  
  Purchase #5 $243.65   7.744%   $262.5183   $262.52   $262.50   $262.50  
  Purchase #6 $206.82   5.589%   $218.3792   $218.38   $218.40   $218.40  
  Purchase #7 $87.41   4.135%   $91.0244   $91.02   $91.00   $91.00  
  7 purchase totals = $950.13       $1,019.8328   $1,019.83   $1,019.85   $1,019.70