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 $232.58   8.354%   $252.0097   $252.01   $252.00   $252.00  
  Purchase #2 $120.68   10.649%   $133.5312   $133.53   $133.55   $133.50  
  Purchase #3 $54.35   9.781%   $59.666   $59.67   $59.65   $59.70  
  Purchase #4 $207.45   13.594%   $235.6508   $235.65   $235.65   $235.70  
  Purchase #5 $97.47   11.363%   $108.5455   $108.55   $108.55   $108.50  
  Purchase #6 $117.50   3.350%   $121.4363   $121.44   $121.45   $121.40  
  Purchase #7 $196.70   7.265%   $210.9903   $210.99   $211.00   $211.00  
  7 purchase totals = $1,026.73       $1,121.8298   $1,121.84   $1,121.85   $1,121.80