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 $202.89   11.838%   $226.9081   $226.91   $226.90   $226.90  
  Purchase #2 $238.58   4.828%   $250.0986   $250.10   $250.10   $250.10  
  Purchase #3 $161.31   4.270%   $168.1979   $168.20   $168.20   $168.20  
  Purchase #4 $90.52   5.335%   $95.3492   $95.35   $95.35   $95.30  
  Purchase #5 $28.68   13.726%   $32.6166   $32.62   $32.60   $32.60  
  Purchase #6 $171.91   5.781%   $181.8481   $181.85   $181.85   $181.80  
  Purchase #7 $219.57   9.728%   $240.9298   $240.93   $240.95   $240.90  
  7 purchase totals = $1,113.46       $1,195.9483   $1,195.96   $1,195.95   $1,195.80