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 $78.54   6.613%   $83.7339   $83.73   $83.75   $83.70  
  Purchase #2 $145.89   10.592%   $161.3427   $161.34   $161.35   $161.30  
  Purchase #3 $113.30   3.595%   $117.3731   $117.37   $117.35   $117.40  
  Purchase #4 $247.89   8.223%   $268.274   $268.27   $268.25   $268.30  
  Purchase #5 $156.67   6.121%   $166.2598   $166.26   $166.25   $166.30  
  Purchase #6 $16.94   6.167%   $17.9847   $17.98   $18.00   $18.00  
  Purchase #7 $202.52   9.401%   $221.5589   $221.56   $221.55   $221.60  
  7 purchase totals = $961.75       $1,036.5271   $1,036.51   $1,036.50   $1,036.60