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 $181.51   13.675%   $206.3315   $206.33   $206.35   $206.30  
  Purchase #2 $32.64   3.421%   $33.7566   $33.76   $33.75   $33.80  
  Purchase #3 $189.56   7.609%   $203.9836   $203.98   $204.00   $204.00  
  Purchase #4 $92.93   9.561%   $101.815   $101.82   $101.80   $101.80  
  Purchase #5 $184.47   10.399%   $203.653   $203.65   $203.65   $203.70  
  Purchase #6 $158.44   12.183%   $177.7427   $177.74   $177.75   $177.70  
  Purchase #7 $147.81   5.249%   $155.5685   $155.57   $155.55   $155.60  
  7 purchase totals = $987.36       $1,082.8509   $1,082.85   $1,082.85   $1,082.90