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 $202.25   11.552%   $225.6139   $225.61   $225.60   $225.60  
  Purchase #2 $98.47   3.623%   $102.0376   $102.04   $102.05   $102.00  
  Purchase #3 $160.92   11.530%   $179.4741   $179.47   $179.45   $179.50  
  Purchase #4 $84.68   10.760%   $93.7916   $93.79   $93.80   $93.80  
  Purchase #5 $219.31   3.873%   $227.8039   $227.80   $227.80   $227.80  
  Purchase #6 $27.56   7.384%   $29.595   $29.60   $29.60   $29.60  
  Purchase #7 $130.28   11.301%   $145.0029   $145.00   $145.00   $145.00  
  7 purchase totals = $923.47       $1,003.3190   $1,003.31   $1,003.30   $1,003.30