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 $48.84   9.338%   $53.4007   $53.40   $53.40   $53.40  
  Purchase #2 $193.56   6.359%   $205.8685   $205.87   $205.85   $205.90  
  Purchase #3 $243.41   4.631%   $254.6823   $254.68   $254.70   $254.70  
  Purchase #4 $194.73   7.570%   $209.4711   $209.47   $209.45   $209.50  
  Purchase #5 $29.25   11.669%   $32.6632   $32.66   $32.65   $32.70  
  Purchase #6 $190.52   12.634%   $214.5903   $214.59   $214.60   $214.60  
  Purchase #7 $129.79   11.312%   $144.4718   $144.47   $144.45   $144.50  
  7 purchase totals = $1,030.10       $1,115.1479   $1,115.14   $1,115.10   $1,115.30