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 $34.77   7.393%   $37.3405   $37.34   $37.35   $37.30  
  Purchase #2 $156.91   11.829%   $175.4709   $175.47   $175.45   $175.50  
  Purchase #3 $6.83   12.742%   $7.7003   $7.70   $7.70   $7.70  
  Purchase #4 $250.65   13.213%   $283.7684   $283.77   $283.75   $283.80  
  Purchase #5 $173.70   11.663%   $193.9586   $193.96   $193.95   $194.00  
  Purchase #6 $84.87   5.865%   $89.8476   $89.85   $89.85   $89.80  
  Purchase #7 $218.54   11.664%   $244.0305   $244.03   $244.05   $244.00  
  7 purchase totals = $926.27       $1,032.1168   $1,032.12   $1,032.10   $1,032.10