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 $22.96   7.778%   $24.7458   $24.75   $24.75   $24.70  
  Purchase #2 $151.36   6.561%   $161.2907   $161.29   $161.30   $161.30  
  Purchase #3 $73.56   11.379%   $81.9304   $81.93   $81.95   $81.90  
  Purchase #4 $207.26   12.384%   $232.9271   $232.93   $232.95   $232.90  
  Purchase #5 $223.39   3.416%   $231.021   $231.02   $231.00   $231.00  
  Purchase #6 $74.92   12.279%   $84.1194   $84.12   $84.10   $84.10  
  Purchase #7 $229.75   6.438%   $244.5413   $244.54   $244.55   $244.50  
  7 purchase totals = $983.20       $1,060.5757   $1,060.58   $1,060.60   $1,060.40