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 $125.73   7.154%   $134.7247   $134.72   $134.70   $134.70  
  Purchase #2 $220.61   3.188%   $227.643   $227.64   $227.65   $227.60  
  Purchase #3 $147.84   7.860%   $159.4602   $159.46   $159.45   $159.50  
  Purchase #4 $216.45   12.770%   $244.0907   $244.09   $244.10   $244.10  
  Purchase #5 $32.52   7.230%   $34.8712   $34.87   $34.85   $34.90  
  Purchase #6 $22.46   13.777%   $25.5543   $25.55   $25.55   $25.60  
  Purchase #7 $194.87   5.676%   $205.9308   $205.93   $205.95   $205.90  
  7 purchase totals = $960.48       $1,032.2749   $1,032.26   $1,032.25   $1,032.30