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 $218.54   4.381%   $228.1142   $228.11   $228.10   $228.10  
  Purchase #2 $212.26   5.363%   $223.6435   $223.64   $223.65   $223.60  
  Purchase #3 $57.92   8.712%   $62.966   $62.97   $62.95   $63.00  
  Purchase #4 $234.29   8.803%   $254.9145   $254.91   $254.90   $254.90  
  Purchase #5 $187.96   3.388%   $194.3281   $194.33   $194.35   $194.30  
  Purchase #6 $51.74   3.346%   $53.4712   $53.47   $53.45   $53.50  
  Purchase #7 $235.31   6.450%   $250.4875   $250.49   $250.50   $250.50  
  7 purchase totals = $1,198.02       $1,267.9250   $1,267.92   $1,267.90   $1,267.90