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 $232.25   13.852%   $264.4213   $264.42   $264.40   $264.40  
  Purchase #2 $22.88   13.823%   $26.0427   $26.04   $26.05   $26.00  
  Purchase #3 $74.39   10.681%   $82.3356   $82.34   $82.35   $82.30  
  Purchase #4 $157.72   9.558%   $172.7949   $172.79   $172.80   $172.80  
  Purchase #5 $102.53   4.683%   $107.3315   $107.33   $107.35   $107.30  
  Purchase #6 $195.52   9.119%   $213.3495   $213.35   $213.35   $213.30  
  Purchase #7 $184.71   3.869%   $191.8564   $191.86   $191.85   $191.90  
  7 purchase totals = $970.00       $1,058.1319   $1,058.13   $1,058.15   $1,058.00