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 $160.79   10.398%   $177.5089   $177.51   $177.50   $177.50  
  Purchase #2 $160.55   3.801%   $166.6525   $166.65   $166.65   $166.70  
  Purchase #3 $57.56   3.807%   $59.7513   $59.75   $59.75   $59.80  
  Purchase #4 $120.78   10.377%   $133.3133   $133.31   $133.30   $133.30  
  Purchase #5 $233.85   11.573%   $260.9135   $260.91   $260.90   $260.90  
  Purchase #6 $31.46   13.407%   $35.6778   $35.68   $35.70   $35.70  
  Purchase #7 $165.58   9.186%   $180.7902   $180.79   $180.80   $180.80  
  7 purchase totals = $930.57       $1,014.6075   $1,014.60   $1,014.60   $1,014.70