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 $77.49   9.601%   $84.9298   $84.93   $84.95   $84.90  
  Purchase #2 $219.63   7.383%   $235.8453   $235.85   $235.85   $235.80  
  Purchase #3 $181.43   6.242%   $192.7549   $192.75   $192.75   $192.80  
  Purchase #4 $14.60   11.823%   $16.3262   $16.33   $16.35   $16.30  
  Purchase #5 $31.33   5.201%   $32.9595   $32.96   $32.95   $33.00  
  Purchase #6 $38.98   6.783%   $41.624   $41.62   $41.60   $41.60  
  Purchase #7 $95.94   5.570%   $101.2839   $101.28   $101.30   $101.30  
  7 purchase totals = $659.40       $705.7236   $705.72   $705.75   $705.70